Trichodinid species from the gill of cultured Japanese eel, Anguilla japonica, with the description of a new species based on light and scanning electron microscopy.

Trichodinid ciliates infested on the gills of cultured Japanese eels, Anguilla japonica, were surveyed. A new species was detected in addition to Trichodina jadranica and T. acuta, and was described as T. japonica n.sp. Scanning electron microscopic observations on the new species revealed an aboral ciliary complex which consisted of long and sparsely arranged marginal cilia, a basal ciliary ring having very short cilia, and a well developed locomotor wreath. A thin anterior septum existed between the marginal ciliary ring and the locomotor ciliary wreath, and a thicker basal septum was observed between the locomotor ciliary wreath and the basal ciliary ring. On the adhesive disc, denticles and radial pins were clearly observed by scanning electron microscopy. The basal membrane, which forms the periphery of the adhesive disc, consisted of three layers. A dented ring caused by attachment of T. japonica was observed on the gill surface of the eel examined.